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Do I Need a New Thermostat for a Variable-Speed AC?

Choosing a thermostat is an important decision. While some thermostats work with several types of heating and cooling systems, others are more specific, so compatibility may be an issue. For example, a variable-speed AC requires a control system with specific functions to access all its features.

Staged heating and cooling is a revolution in HVAC technology. Years ago, air conditioners and furnaces could only be turned on or off. When on, they simply ran at full capacity all the time. Today’s energy-efficient alternatives have moved beyond single-stage heating and cooling to two-stage performance (at 100% capacity or usually 65% capacity) to variable-speed systems. These can typically operate at any level between 40% and 100% to adjust to demand.

How Variable-Capacity Thermostats Differ from Two-Stage and Single-Stage Thermostats

Communicating thermostats, as variable-capacity models are called, differ from other models that use specific wires to send signals to control performance. A variable-capacity thermostat has four wires: one wire for heating, one wire for cooling, and two wires that provide power and allow communication between the thermostat and other HVAC components. 

Temperature sensors throughout the system send data to the thermostat. The unit can adjust specific components to provide precise heating or cooling control. This keeps your home at the desired temperature within a tight margin. While variable-speed blower fans adjust automatically, the thermostat may let you adjust the fan speed manually from the control panel or touchscreen.

Therefore, installing a new thermostat for a variable-speed AC is a very good idea.

Determining Compatibility with Your AC System

Compatibility is an important consideration. A non-communicating thermostat can have up to 12 wires, and a Wi-Fi thermostat will also have a C wire. If you see only four wires in the unit, it’s a communicating thermostat and will have white, yellow, green, and red terminal connections. However, single-stage systems have the same configuration, so they can be confused with a communicating thermostat.

A communicating model is made directly by the manufacturer of your AC. Honeywell, GE, Emerson, and other brands are popular and make quality thermostats, but they do not manufacture HVAC equipment. Look for ComfortNet by Amana, Goodman, and Daikin. Other communicating thermostats are made by Bryant (Evolution), Carrier (Infinity), Lennox (iComfort), Rheem (Comfort Control System), and Trane (ComfortLink II).

Here is how to determine if the thermostat you’re buying is compatible with your variable-speed AC:

  • The thermostat comes with the unit or carries the same name.
  • A thermostat’s product description reads “Works with 2-stage or multi-stage heat or cool”.
  • Use the manufacturer’s online compatibility checker; selecting colors from the chart (representing the wires your current device has) reveals whether your current thermostat is compatible.

If your new AC doesn’t come with one, purchase a thermostat from a local dealer that supplies equipment from the same brand.

Features for Controlling Your Variable Speed AC

A communicating thermostat can be programmable. A programmable model lets you adjust temperature settings automatically based on the time of day. For example, you can set the temperature at one level for weekdays and another for weekends or depending on when you’re home, away, or asleep. Depending on your routine, they can save on energy costs.

Wi-Fi/smart thermostats are programmable and allow you to remotely monitor and control your HVAC system. A smartphone app lets you access it from anywhere. This is especially convenient if your schedule often changes. Some systems can also track you based on your phone’s location. The most advanced Wi-Fi touchscreen thermostats offer precise control and display weather conditions.

However, zone thermostats provide independent climate control for different rooms in your home. If one is compatible with your variable-speed AC, you can use it to provide more heating or cooling to living areas or bedrooms, depending on which are being used. You’ll need a zoned communicating thermostat if you have a zoned HVAC system.

If this sounds confusing, your local HVAC installer can answer your questions and provide advice.

Contact Monarch Home Services

If you install a variable-speed AC, you’ll likely need a new thermostat. There are more options for thermostats than ever before. We can help you determine the best type for your needs and understand how you can benefit from a communicating thermostat. For advice from our AC replacement and installation professionals, to receive a free quote, or to schedule an appointment in your Fresno or Bakersfield home, call (661) 215-5851 today.

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